Synthesis, characterization and crystal structure of a monomeric and a macrocyclic copper (II) complex with a large cavity using benzylacetylacetone ligand

Article abstract of DOI:10.1016/j.ica.2003.12.014

The bidentate ligand benzylacetylacetone was used to synthesize the Cu(II) complexes 1 and 2 without and with 4,4^′-bipyridine ligand, respectively. The complexes were characterized by analytical and spectroscopic studies. The mononuclear complex [Cu(C₁₀H₉O ₂)₂] (1) has been synthesized by the reaction of copper acetate with the ligand whereas the tetranuclear complex [Cu₄(4, 4^′-bpy)₄(C₁₀H₉O ₂)₄(C₂H₃O₂)₄] (2) has been synthesized by the reaction of copper acetate with the ligand followed by the addition of 4,4^′-bipyridine. The X-ray analysis shows that the complex 1 has square planar geometry and the complex 2 has square pyramidal geometry around the metal centers. The thermogravimetric studies showed that the complexes undergo decomposition in multiple steps.

Full text of DOI:10.1016/j.ica.2003.12.014

Inorganica Chimica Acta 357 (2004) 1991–1996
www.elsevier.com/locate/ica
Synthesis, characterization and crystal structure of a monomeric
and a macrocyclic copper (II) complex with a large cavity using
benzylacetylacetone ligand q
a
Subrata Kumar Dey , Bappaditya Bag , Zhongyuan Zhou , Albert S.C. Chan ,
a
b
b
a,
*
Samiran Mitra
a
Department of Chemistry, Jadavpur University, Kolkata 700 032, West Bengal, India
b
Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Kowloon, Hong Kong
Received 2 July 2003; accepted 13 December 2003
Abstract
The bidentate ligand benzylacetylacetone was used to synthesize the Cu(II) complexes 1 and 2 without and with 4,40-bipyridine
ligand, respectively. The complexes were characterized by analytical and spectroscopic studies. The mononuclear complex
[Cu(C10H9O2)2] (1) has been synthesized by the reaction of copper acetate with the ligand whereas the tetranuclear complex
[Cu4(4,40-bpy)4(C10H9O2)4(C2H3O2)4] (2) has been synthesized by the reaction of copper acetate with the ligand followed by the
addition of 4,40-bipyridine. The X-ray analysis shows that the complex 1 has square planar geometry and the complex 2 has square
pyramidal geometry around the metal centers. The thermogravimetric studies showed that the complexes undergo decomposition in
multiple steps.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Cu(II) monomeric and macrocyclic complexes; Benzylacetylacetone; 4,40-Bipyridine; Crystal structures
1. Introduction
ganic ‘‘spacer’’ ligand [6–8]. In the supramolecular
chemistry of hydrogen-bonded organic molecule, coor-
dination polymers [9] offer a higher potential because of
the variety of coordination modes and the peculiarities
of the metallic centers. Extending the scope of the
crystal engineering to self-assembled metal systems
containing two different organic ligands is much less
explored, and it is generally not yet possible to predict
either the composition or structure of the product of a
reaction consisting of a metal center and two different
organic ligands.
The deliberate design of a novel networks based on
coordination compounds requires a careful selection of
the polydentate ligand. In the present study, the syn-
thesis of mononuclear four coordinated Cu(II) complex
[Cu(C10H9O2)2] (1) and 4,40-bipyridine bridged tetra-
nuclear complex [Cu4(4,40-bpy)4 (C10H9O2)4 (C2H3O2)4]
(2) have been reported. Spectroscopic and thermal
properties have been investigated for both the complexes
along with the X-ray crystal structures.
The ability of 4,40-bipyridine (4,40-bpy) and pyrazine
(pyz) to act as exo-bidentate ligands, thus giving rise to
the formation of oligomeric and polymeric metal com-
plexes, is well established [1–4]. Furthermore, supra-
molecular chemistry and self-assembly with 4,40-bpy,
pyz and their derivatives are at the frontiers of molec-
ular science, as demonstrated by the intense interest and
near exponential growth of publications in this area in
the last decade [5]. Many examples exist of 4,40-bpy and
pyz acting as a linear spacer between metal centers to
form 1D-chain polymers and 2D square lattice, and
three-dimensional (3D) motifs with rigid multitopic or-
q Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.ica.2003.12.014.
* Corresponding author. Tel.: +91-33-2668-2017/2414-6193; fax:
+91-33-2414-6266.
E-mail address: smitra_2002@yahoo.com (S. Mitra).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.12.014

1992
S.K. Dey et al. / Inorganica Chimica Acta 357 (2004) 1991–1996
2. Experimental
2.1. Materials
shaped crystals after 10 h. The crystals were washed with
methanol and air-dried. Yield: 45%. Anal. Calc. for
C88H80Cu4N8O16: C, 60.0; H, 4.58; N, 3.19; Cu, 14.44.
Found: C, 60.12; H, 4.60; N, 3.17; Cu, 14.49%.
Benzylacetylacetone, copper acetate (Merck), were
used as received.
2.3. Physical measurements
2.2. Synthesis of the complex 1 and 2
Elemental analyses were carried out using a Perkin–
Elmer 2400 II elemental analyzer. Infrared spectra were
recorded on a Perkin–Elmer 883-IR spectrophotometer
using KBr pellets as well as in solution. Electronic
spectra were recorded on a Lamda-40 spectrophotome-
ter. Thermal investigations (TGA) were carried out on a
Shimadzu TGA-50 thermal analyser under a dynamic
2.2.1. [Cu(C10H9O2)2] (1)
The complex 1 was synthesised by slowly adding a
suspension of benzylacetylacetone (2 mmol) in 10 ml
methanol to a 15 ml methanolic solution of copper ac-
etate (0.199 g, 1 mmol) at room temperature with con-
stant stirring. Shiny green rod like crystals appeared
after 8 h, from which suitable crystals for X-ray analysis
were separated. Yield: 54%. Anal. Calc. for
C20H18CuO4: C, 62.19; H, 5.05; Cu, 16.47. Found: C,
62.20; H, 5.14; Cu, 16.55%.
The complex [Cu4(C22H20N2O4)4] (2) was prepared
by slowly adding a 20 ml methanolic suspension of
benzylacetylacetone (1 mmol) to a 20 ml methanolic
solution of copper acetate (0.199 g, 1 mmol) at room
temperature with constant stirring. To this resulting
solution, 4,40-bipyridine (1 mmol) in 15 ml methanol
was added slowly and the resulting mixture was kept at
room temperature, which afforded green colored needle
1
nitrogen environment. H NMR spectra was recorded
on a Bruker DPX-300 (300 MHz) NMR spectrometer in
CDCl3 using tetramethyl silane (TMS) as internal ref-
erence. The magnetic susceptibility were measured for
the solid samples at room temperature using a vibrating
sample magnetometer using mercury (tetrathiocyanato)
cobaltate as a standard.
2.4. X-ray data collection and structure refinement
The pale blue needle shaped crystals of 1 (size
0.30 ꢀ 0.06 ꢀ 0.04 mm3) and deep green needle shaped
crystals of 2 (size 0.38 ꢀ 0.10 ꢀ 0.08 mm3) were mounted
Table 1
Crystal data and structure refinement for 1 and 2
1
2
Empirical formula
Formula weight
Temperature (K)
Cu(C10H9O2)2
385.88
294(2)
(CuC22H20N2O4)4
1759.76
294(2)
ꢀ
Wavelength (A)
0.71073
monoclinic
P21=n
0.71073
tetragonal
Crystal system
Space group
Unit cell dimensions
ꢁ
I4
ꢀ
a (A)
4.472(13)
10.616(3)
18.435(5)
96.412(4)
869.7(4)
2
22.466(2)
22.466(2)
7.472(11)
ꢀ
b (A)
ꢀ
c (A)
b (°)
Volume (A )
3
ꢀ
3771.2(8)
2
Z
Density (Calc.) (Mg/m3)
Absorption coefficient (mmꢁ1
F ð000Þ
1.473
1.277
1.550
1.191
1816
)
398
0.30 ꢀ 0.06 ꢀ 0.04
Crystal size (mm3)
h Range for data collection
Limiting indices
0.38 ꢀ 0.10 ꢀ 0.08
2.94–27.54°
2.87–27.52°
ꢁ5 6 h 6 5, ꢁ13 6 k 6 13,
ꢁ18 6 1 6 23
ꢁ27 6 h 6 29, ꢁ29 6 k 6 27,
ꢁ9 6 l 6 9
Reflections collected
Independent reflections (Rint
Refinement method
5721
1983 (0.0607)
12 835
4319 (0.0451)
)
full-matrix least-squares on F2
1983/0/116
1.030
full-matrix least-squares on F2
4319/0/264
1.020
Data/restrains/parameters
Goodness-of-fit on F2
Final R indices [I > 2rðIÞ]
R indices (all data)
R1 ¼ 0:0679, wR2 ¼ 0:1590
R1 ¼ 0:1208, wR2 ¼ 0:1782
0.744 and )0.559
R1 ¼ 0:0465, wR2 ¼ 0:1085
R1 ¼ 0:0776, wR2 ¼ 0:1202
0.579 and )0.380
ꢁ3
ꢀ
Largest difference in peak and hole (e A
)

S.K. Dey et al. / Inorganica Chimica Acta 357 (2004) 1991–1996
1993
on a fine-focus sealed tube of Bruker SMART CCD
area detector. The Crystallographic data of 1 and 2 are
listed in Table 1. Cell dimension and intensity data for
the crystal 1 and 2 were measured at 294(2) K, fitted
with graphite-monochromated Mo Ka radiation,
range 649 cmꢁ1, which assigned for d–d transition and
supports the four coordinated square planar geometry
around the copper (II) ion with the CuO4 chromophoric
group. The electronic spectrum of the complex 2 in
CH2Cl2 solution exhibits a sharp band at 860 nm and a
broad band with a maximum at 682 nm, characteristic
of a distorted square pyramidal CuN2O3 coordination
polyhedron [15].
ꢀ
k ¼ 0:71073 A. For 1, a total of 5721 reflections in the h
range 2.94–27.54° were collected using x scans, of these
1983
were
independent,
and
satisfied
the
I > 2rðIÞ½Rint ¼ 0:0607] criterion of observability and
were used in the subsequent structure determination and
refinement. For 2, total of 12 835 reflections in the h
range 2.87–27.52° were collected using u and x scans, of
these 4319 were independent, and satisfied the
I > 2rðIÞ½Rint ¼ 0:0451] criterion of observability and
were used in the subsequent structure determination and
refinement. The semi-empirical absorption was applied.
3.3. NMR spectra
The 1H NMR spectra of the copper(II) complexes
derived from bidentate ligands have been recorded in
CDCl3. The 1H NMR spectra of the complexes support
the stoichiometric formula [Cu(C10H9O2)2] (1) and
[Cu4(4,40-bpy)4(C10H9O2)4(C2H3O2)4] (2). The aromatic
and aliphatic proton signals are in their usual positions.
The structures were solved by direct methods (SHELXS
-
97) [10] and refined on F2 by full-matrix least-squares
using all unique data (SHELXL-97) [11]. All the non-
hydrogen atoms were refined anisotropically. The final
R indices were 0.0679 and 0.1590 for 1, 0.0465 and
0.1085 for 2, respectively, for all observed reflections.
Maximum and minimum peaks in the final difference
Fourier synthesis were 0.744 and )0.599 for 1, 0.579 and
)0.380 for 2 e Aꢁ3, respectively.
In the H NMR spectrum of the free ligand, the reso-
nance signal due to the free OH group appears at d 12.4
ppm. This signal is not present in the H NMR spectra
1
1
of the copper (II) complexes. This confirms that the
bonding of the ligand oxygen atoms to Cu(II) occur
through the replacement of alcoholic hydrogen, further
supporting the observation recorded in infrared spectra.
3.4. Thermal studies
3. Results and discussion
The thermogravimetric analyses of the complex 1 and
2 have been carried out non-isothermally under a flow of
dry N2. The complex 1 is stable up to 145 °C and 2 is
stable up to 160 °C. The mass loss in the TGA curve
corresponds to the release of coordinated acetate groups
from 2 followed by the loss of the 4,40-bpy molecules in
between 161 and 275 °C. On further heating up to 510
°C the oxide residue is left, confirmed by qualitative test.
The mass loss in the TGA curve corresponds to the re-
lease of two coordinated ligands from 1 between 146 and
450 °C resulting the oxide residue confirmed by quali-
tative test.
3.1. Infrared spectra
A weak broad band in the region 3150–3300 cmꢁ1
due to OH group in free ligand (in solution) was not
observed in the infrared spectra of complex 1 and 2. This
indicates that the alcoholic oxygen is deprotonated and
coordinated with Cu(II). Carboxylate groups can coor-
dinate to metals in syn–syn, anti–anti, and syn–anti and
in monoatomic fashion [12]. The bands of mas (COꢁ2 ) at
1680 cmꢁ1 and ms (COꢁ2 ) at 1370 cmꢁ1, respectively,
having 310 cmꢁ1 separation value (DmÞ [12], is signifi-
cantly higher than the free carboxylate group indicating
the carboxylate group is coordinated with Cu in a
monodentate fashion [13], which is unambiguously
confirmed by the crystal structure of 2. The bands at
1596, 1535, 1414, 1224, 1074, 1028, 995, 822 cmꢁ1 in-
dicated the presence of 4,40-bipyridine for complex 2.
The m(Cu–O) and all other bands appeared at their usual
positions.
3.5. Magnetic moment
The room temperature magnetic moment of the
compound 1 is 1.74lB fits well with the spin only value
for the copper (II) system. The magnetic moment value
per copper atom of the compound 2 is 1.76lB at RT
slightly higher than the expected value for one unpaired
electrons on each.
3.2. Electronic spectra
3.6. Description of the structures
Although the electronic spectra of the copper com-
plexes with multidentate Schiff base ligands are not in
general good indicators of geometry [14], but help to
support it. The spectrum of the complex 1 was recorded
in chloroform. For the complex 1, bands appeared in the
The crystal structure of complex 1 consists of mo-
nomeric [Cu(C10H9O2)2] units is shown in Fig. 1 and the
molecular packing diagram is shown in Fig. 2, the bond
distances and angles are given in the Table 2. Complex 1
crystallizes in monoclinic system with space group

1994
S.K. Dey et al. / Inorganica Chimica Acta 357 (2004) 1991–1996
P21=n. The coordination geometry around the Cu(II)
ion is square planar with four oxygen donor set arising
from two bidentate ligands and the central copper atom
is sitting on the inversion center of symmetry. The mean
deviation of the plane formed by Cu1, O1, O1A, O2 and
ꢀ
O2A is 0, 0, 0, 0 A. The displacement of the atoms O1,
ꢀ
O1A, O2, O2A from the best plane are 0, 0, 0, 0 A,
respectively. The six-membered chelate rings formed by
the ligand moiety with the Cu(II) ion are approximately
ꢀ
coplanar (mean deviation from the plane is 0.0322 A).
The other angles for O1–Cu1–O2A and O1–Cu1–O2 are
lying in between 86.84(12)°–93.16(12)°, respectively.
Two sets of bond distances are equal and comparable to
the other Cu(II) square planar complexes [16,17].
[Cu4(4,40-bpy)4(C10H9O2)4(C2H3O2)4] (2)
Fig. 1. Perspective view of the complex 1 with atom labeling scheme.
A perspective view of the molecule with atom num-
bering scheme is shown in Fig. 3 and the molecular
packing diagram is shown in Fig. 4 and the bond dis-
tances and bond angles are listed in Table 2. The com-
plex has tetra-nuclear unit formed by Cu(II) atom with
crystallographic centre of inversion as shown in Fig. 3.
The local geometry around each copper atom is dis-
torted square pyramidal which comprises the coordinate
plane formed by two nitrogen atoms from two bridging
4,40-bpy (N2 and N3A), one oxygen (O2) from free ac-
etate ion and two oxygen atoms (O1 and O4) from the
ligand. The environment around all the copper atoms
are same. 4,40-bpy and two oxygen atoms from the li-
gand occupy the basal plane and the axial position is
occupied by the acetate ion. In the crystal lattice all the
copper atoms have distorted square pyramidal geometry
with the geometrical factor s ¼ 2:7° for Cu1 (it is same
for all the Cu atoms).
Fig. 2. Molecular packing diagram of complex 1.
Table 2
ꢀ
Bond lengths (A) and angles (°) for 1 and 2
1
Cu1–O1
Cu1–O2
1.924(3)
1.918(3)
Cu1–O1A
Cu1–O2A
1.924(3)
1.918(3)
O1–Cu1–O1A
O2A–Cu1–O1A
O2–Cu1–O1A
180.00(1)
93.16(12)
86.84(12)
O1–Cu1–O2
O1–Cu1–O2A
O2–Cu1–O2A
93.16(12)
86.84(12)
180.00(1)
2
Cu1–O1
1.920(3)
2.015(3)
2.438(3)
Cu1–O4
Cu1–N2
1.942(3)
2.051(3)
Cu1–N3A
Cu1–O2
O1–Cu1–O4
O4–Cu1–N3A
O4–Cu1–N2
O1–Cu1–O2
N3A–Cu1–O2
91.92(10)
86.23(12)
174.03(19)
88.08(16)
97.10(16)
O1–Cu1–N3A
O1–Cu1–N2
N3A–Cu1–N2
O4–Cu1–O2
N2–Cu1–O2
174.6(2)
88.05(11)
93.26(12)
92.87(15)
93.10(16)
Fig. 3. Perspective view of the complex 2 with atom labeling scheme.

S.K. Dey et al. / Inorganica Chimica Acta 357 (2004) 1991–1996
1995
CB2 1EZ, UK (fax: +44-1223-336033; deposit@ccdc.
cam.ac.uk or www.ccdc.cam.ac.uk).
Acknowledgements
We thank the Council of Scientific and Industrial
Research, New Delhi, India for financial assistance to
Dr. S.K. Dey. Thanks may also be extended to UGC,
New Delhi, India for financial assistance.
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